Aperture blades appear wet/greasy on second-hand lens?

[matt_giess]

Hi all

 

I've found a bargain used Pentax f-series prime lens, all the optics

are clean and fungus free but there's a problem with the aperture.

It was quite stiff and didn't spring back. The dealer (who I trust)

assures me that it is simply due to return spring breaking, and he'll

fix it for me. However, some of the aperture blades appear greasy,

almost damp, and I noticed in a previous discussion on fungus in

lenses that 'Heat could also cause the grease in the helicoid to melt

and make the aperture sticky' - could this also be the case here?

Would this contribute to the broken spring, and will this be a

recurring problem?

 

I'd really like to buy the lens, as Pentax A/F primes are rare and

very expensive and this is very cheap, but obviously I'd like to

avoid ruined ones!.

 

All advice gratefully received

 

Matt

[art_haykin]

It may, repeat MAY turn out not to be a broken spring, but rather, sticky blades. However, if the dealer will fix and guarantee it, go ahead. The blades should appear 'dry.'

[art_karr]

Matt:

 

Don't know what is wrong with this particular lens but I have had

one similar experience. I bought a new Nikon 55mm f/2.8 [which

I later found has become famous for lubricant bleed to the

blades]. I had it cleaned two times by Nikon. It usually worked for

one year before the problem happened again. I eventually gave

up on the private recommendation of someone from Nikon.

Glass is still good and on a good day I can use it in the

stop-down mode. ;<)

 

Art

[henry_cheng3]

I believe that it is a lubricant leak. It will gum up the aperture blades and make them stick. I once bought a used nikon 50mm with this problem. It was not long before the diaphragm no longer functioned.

[gary_watson]

As Art Karr noted in reference to the 55/2.8, leakage is a baked-in problem with some lenses. Though this may also be true of your Pentax, I suspect the lens is a victim of amateur surgery. Even if the seller promises to fix a busted spring, the blades won't get any less gicky and they will eventually hang up, leaving you with a useless "bargain" lens--some bargain... Keep looking and be patient. There's really no such thing as a "fixer-upper" lens.

[pete_andrews]

Sorry to disagree Gary, but most of my extensive screw-fit Zeiss Jena and Takumar glass collection has been 'fixed-up' from stuck diaphram bargains. You just have to be prepared to completely strip the lens down to the iris blades and then thoroughly degrease them in alcohol.<br>Takes me about 2 hours per lens on average, but I rarely have to repeat the procedure.<p>I also don't believe that all of the oil I find has crept out of the helicoid grease. In some cases it's definitely the result of a misguided attempt at an amateur 'CLA'.